This invention relates to the microstepping control of a unipolar stepping motor.
The inventors' U.S. Pat. No. 4,855,660, commonly assigned, discloses a novel means and method for microstepping of a unipolar stepping motor. The disclosed embodiment of the present invention represents an improvement in regulating the current delivered to the motor.
Conventional current regulation requires directly sensing the current in a motor winding via a sense resistor, Hall sensor, or current transformer. These are wasteful of power and voltage delivery to the motor.
The present invention involves the sensing of motor current indirectly through the measurement of voltage and winding resistance. More specifically, the invention involves the sensing of motor voltage by sensing battery voltage and the sensing of winding resistance by sensing winding temperature. From the measurement of these parameters, the required pulse width modulated (PWM) duty cycle can be calculated for the desired motor current. Advantages of the invention include lower cost, lower voltage drop, smaller size, and lower power dissipation.
The foregoing, along with other advantages, of the invention will be seen in the ensuing description and claims which should be considered in conjunction with the accompanying drawings. The drawings disclose a presently preferred embodiment of the invention according to the best mode contemplated at the present time for carrying out the invention.